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tda1387 dac pcb "front end"
tda1387 dac pcb "front end"
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Old 21st December 2017, 05:25 PM   #31
matt_garman is offline matt_garman  United States
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tda1387 dac pcb "front end"
Quote:
Originally Posted by abraxalito View Post
the TL431 reference can be shared between the two I/V transistors. This'll save you a few parts - each transistor needs its own 22ohm base resistor but beyond that you only need one instance of the voltage reference.
Can the TL431 reference be shared between four I/V transistors (as in the balanced design)?

Any update on your lingDAC?
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Old 21st December 2017, 05:50 PM   #32
Mayday is offline Mayday  Sweden
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tda1387 dac pcb "front end"
Quote:
Originally Posted by matt_garman View Post
Here's revision 1.1 of the single-ended RPi HAT. I fixed the tda1387 footprint, and also simplified the tl431 voltage reference per Abraxalito's suggestion.

The only other change was to add resistors in front of the tda1387's I2S input pins (1/BCK, 2/WS, 3/DATA). Not sure if that's really necessary, and if so, what the values should be... easy enough to use a 0R if they don't need to be there.

These KiCAD raytraced renders look better than the real thing IMO!
That looks really nice, KiCad is a great tool.
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Old 21st December 2017, 06:45 PM   #33
Malefoda is offline Malefoda  France
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Very nice! I'm in a bush ready to jump!
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Old 22nd December 2017, 12:48 AM   #34
abraxalito is offline abraxalito  United Kingdom
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Quote:
Originally Posted by matt_garman View Post
Can the TL431 reference be shared between four I/V transistors (as in the balanced design)?
Yes sure, why not? According to LTspice the base current is plenty low enough not to load the reference significantly.

Quote:
Any update on your lingDAC?
I'm still playing with the design, not trying to get it to sound better as I'm completely satisfied with the sound, rather I want to know if I can make it easier to build. And perhaps cheaper too, also lower power.

I've built about 5 USB input lingDACs, sent the first one out for listening evaluation yesterday. They are all based on this Taobao DAC (because its super-cheap) : L1387DAC 4X ??TDA1387 ??USB???(??+??),??TDA1543-???

I've made one S/PDIF input version and have three more of these in the pipe for construction. These are powered by an external source - an 18650 Li-ion cell for example and based on the mechanics of this DAC : ????????????????apple tv3 SPDIF??PCM5102A-???
On this 95rmb DAC I'm disconnecting the PCM5102A but still using the AK4113 S/PDIF receiver. Most of the through-hole passives I remove (lots of small 'lytics and polyester caps) and replace with SMT ceramics on the other side of the PCB to save top side space. There might even be enough room to fit a headphone amp - there's a 3.5mm output socket as well as the RCAs.
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Old 24th December 2017, 05:10 PM   #35
matt_garman is offline matt_garman  United States
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tda1387 dac pcb "front end"
Default Front End v2.0

I re-designed the 8x front-end board. Mostly just for fun, original design was done in Eagle, and I've since moved to KiCad entirely. Also, the original board had a few annoyances: bottom-mounting of some components, a couple inconsistently-sized components, no easy way to combine outputs when running in single-ended mode, and only one giant ground plane. Version 2 addresses all that.
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Old 24th December 2017, 05:21 PM   #36
matt_garman is offline matt_garman  United States
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tda1387 dac pcb "front end"
Currently waiting to receive the single-ended RPI HAT boards shown above (with the corrected tda1387 footprint). Assuming that works as expected, next step will be to have this fabbed, a balanced version. This is something I've wanted for a while, a cheap, balanced NOS RPI DAC-HAT. Not too many of these that I've seen.
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Old 1st January 2018, 12:27 PM   #37
robert1325 is offline robert1325  Netherlands
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Have you had a chance to compare your front end to the 8x dac yet? I'm curious to hear what the tda1387 sounds like without the op amps.
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Old 1st January 2018, 12:36 PM   #38
abraxalito is offline abraxalito  United Kingdom
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Extremely good - when implemented with a filter as well as active I/V.
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Old 1st January 2018, 12:50 PM   #39
didiet78 is offline didiet78  Indonesia
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Quote:
Originally Posted by matt_garman View Post
Currently waiting to receive the single-ended RPI HAT boards shown above (with the corrected tda1387 footprint). Assuming that works as expected, next step will be to have this fabbed, a balanced version. This is something I've wanted for a while, a cheap, balanced NOS RPI DAC-HAT. Not too many of these that I've seen.
Add i2c pin and some gpio pin.
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Old 1st January 2018, 03:37 PM   #40
matt_garman is offline matt_garman  United States
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tda1387 dac pcb "front end"
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Originally Posted by robert1325 View Post
Have you had a chance to compare your front end to the 8x dac yet? I'm curious to hear what the tda1387 sounds like without the op amps.
I have not... My modded x8 DAC (the opamp based one from the other thread) has a noise issue that I never got around to debugging. Rather than fix it, I just designed a whole new DAC.

But, based on hearsay (mostly abraxalito's numerous writings on this chip) - passive IV demands a really good power supply, and also is sensitive to downstream components... If that is true, then it implies results will vary significantly from one system to the next.

If you're in the states, it's cheap to ship a board or two to you (I still have several I'm happy to give away).

I'd be willing to part with one of the built up boards too (just not for free). PM me if interested.
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